The present invention relates to a vertical die casting machine or press of the general type manufactured by Applicant's assignee, THT Presses, Inc. In this type press, a frame supports a lower stationary platen and a movable upper platen, and the platens support corresponding lower and upper molds which cooperate to define one or more part defining cavities. The lower platen supports a vertical shot sleeve or cylinder which encloses a shot piston, and the piston moves vertically between a lower retracted position and an upper injection position by a rod extending upwardly from a vertical hydraulic cylinder. The upper platen moves vertically between a lower mold closed position and an upper retracted mold open position by another hydraulic cylinder or set of cylinders.
After the lower mold is shifted laterally on the lower platen by a hydraulic cylinder and the shot piston is retracted downwardly, molten die cast metal or material is poured from an automatically controlled ladle into the chamber defined within the shot cylinder above the shot piston. The lower mold is then shifted laterally to align one or more sprue passages with the shot chamber. The upper platen moves downwardly to close and clamp the upper mold against the lower mold or against a cavity defining part such as a motor rotor confined between the upper and lower molds. The cavity is evacuated, and the shot piston is forced upwardly to inject the molten metal into the mold cavity or cavities. The molds and shot piston are then cooled by circulating water through passages within the molds and shot piston to solidify the die cast material. After the mold is opened, the sprues are retracted downwardly from the lower mold by a sprue connecting biscuit releasably attached to the shot piston. The lower mold is shifted laterally after which the shot piston moves upwardly to provide for removing the sprues and connecting biscuit from the shot piston. The cycle is then repeated for die casting another part or set of parts.
Another form of vertical die casting machine or press is manufactured by Wickes Machinery, a division of The Wickes Corporation. In this die casting machine or press, the molten metal is sucked upwardly through a transfer tube into the shot cylinder by applying a vacuum to the mold cavity. The vacuum also evacuates air from the die cavity or cavities, and the atmospheric air pressure on the molten metal within the furnace pot creates a differential pressure which forces the molten metal upwardly into the shot sleeve. A shot piston then injects the molten metal into the mold cavity or cavities.
In any type of horizontal or vertical die casting machine or press, it is desirable to minimize the cycle time of the die casting operation and to produce high quality parts without voids or porosity. It is also desirable to provide for minimizing the amount of die cast material which solidifies outside the mold cavities in the sprues and mold runners after each cycle is completed. It is also desirable to minimize the pressure at which the molten material is injected into the mold cavities in order to reduce the loading on the press components and the molds and thereby maximize the useful service life of the press and molds.